ARS | Publication request: Modeling Fluvial Response to In-stream Woody Vegetation: Implications for Stream Corridor Restoration

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 26, 2007
Publication Date: September 11, 2007
Citation: Bennett, S.J., Wu, W., Alonso, C.V., Wang, S.S. 2008. Modeling Fluvial Response to In-stream Woody Vegetation: Implications for Stream Corridor Restoration. Earth Surface Processes and Landforms, 33: 890-909.

Interpretive Summary: Degraded streams in northern Mississippi are characterized by flashy hydrographs, banks that are steep and prone to failure, excessive sediment loads, channels that are straight and wide, beds composed of sand, sand and gravel, or cohesive clay, corridors lacking woody debris, and baseflows that are shallow in depth. Moreover, many of the riparian zones are denuded due to agricultural practices, or the channel is so wide that any vegetation present provides little canopy. Transforming a straight, degraded stream into a meandering channel through the use of vegetation should enhance greatly the functionality and recreational opportunities of the corridor. While many studies have discussed the effects of riparian vegetation on flow and transported sediment load in rivers, none has utilized vegetation for the purpose of inducing a straight stream to meander. This approach was first experimentally investigated in a test channel by systematically vegetating a straight, degraded channel with freely adjustable banks and bed to document the effects of vegetation density on alluvial response and morphology. The results were compared to a recently developed numerical model capable of simulating flow, sediment transport, and bed morphology in meandering streams with riparian and in-stream vegetation. It was showed that a straight, degraded stream channel could adopt a meandering thalweg by introducing rigid, emergent vegetation like willow posts at the prescribed spacing of equilibrium meander beds.

Technical Abstract: River restoration and bank stabilization programs often use vegetation for improving stream corridor habitat, aesthetic, and function. Yet no study has examined the use of managed vegetation plantings to transform a straight, degraded stream corridor into a more functional, aesthetically-pleasing meandering channel. Experimental data using a distorted Froude-scaled flume analysis shows that channel expansion and widening, thalweg meandering, and riffle and pool devlopement is possible using discrete plantings of rigid, emergent vegetation. These results were verified and validated using a recently developed numerical model. A hybrid method of meander design is proposed herein where managed vegetation plantings are used to trigger the desired morphologic response, transforming a straight, degraded reach into a more functional meandering corridor.